Threaded tubular connection with progressive axial thread interference

ABSTRACT

A threaded connection includes at least one contact zone axially separated from threadings in which a male and female elements are in sealed contact via bearing surfaces respectively constituted by a cambered surface and by a tapered surface. Such a contact zone ensures a seal against fluids despite positional inaccuracies in the male and female elements at the end of makeup, due to the geometrical characteristics of the threadings. Such a threaded connection can find, as an example, application to oil and gas wells.

The invention relates to a threaded tubular connection comprising a maletubular element comprising a male threading and a female tubular elementcomprising a female threading which cooperates by makeup with said malethreading, the axial width of the threads of said threadings and/or theintervals between said threads varying progressively along the axis ofthe connection over at least a portion of the axial length of thethreadings, such that the threads of each threading are housed with anaxial clearance in the intervals of the other threading at the start ofmakeup, said clearance progressively decreasing until it becomes zeroduring makeup.

The term “sealed contact” as used here means contact between twosurfaces pressed hard against each other to produce a metal-to-metalseal, in particular a gas-tight seal.

Threaded connections of this type are well known, in particular for usein oil and gas wells. They generally have threads with a dovetailprofile as described, for example, in U.S. Re 30,647 and U.S. Re 34,467.They suffer from a number of drawbacks. Firstly, the geometricalcharacteristics of progressive interfering threads cannot ensure agas-tight seal. Such a seal is difficult to obtain with abutmentsurfaces separate from the threadings; sealing surfaces demand veryaccurate relative positioning of the two elements at the end of makeup.However, the final relative position of the elements is in this casestrongly influenced by the machining tolerances for the threads. The useof tapered sealing surfaces with a small taper and thus a small vertexangle, which are more tolerant as regards axial position, does notconstitute a satisfactory solution as such bearing surfaces areextremely sensitive to the phenomenon of galling, which result inspoiling after only a few makeup-breakout operations.

A further disadvantage of said known threaded connections is that thegeometric characteristics of the threadings do not encourage evacuationof the lubrication grease used for makeup. This grease can accumulatelocally, for example between the thread crests and roots, giving rise tovery high pressures which in their turn perturb proper positioning ofthe elements and contact of the sealing surfaces.

The invention aims to eliminate all of the drawbacks mentioned above andto maximize the axial effective contact length under load (internal orexternal pressure, axial tension or compression) of the sealingsurfaces.

The invention also aims to provide a threaded connection that resistscyclic mechanical loads (fatigue).

To this end, the invention provides a threaded connection of the typedefined in the introduction, comprising at least one contact zoneaxially separated from said threadings, in which the male and femaleelements are in sealed contact by means of bearing surfaces respectivelyconstituted by a cambered surface and by a tapered surface.

It has been shown that such a contact zone, which is known per se,allows a substantial variation in the axial position of the contact zoneand thus in the relative position of the elements without losing thegas-tight seal, the effective length of the contact zone or the integralof the contact pressure along the contact zone being high (contactstability).

Optional characteristics of the invention, which may be complementary orsubstitutional, are defined below:

-   -   The cambered surface has a generatrix with a radius of curvature        in the range 30 to 80 mm.    -   The tangent to the vertex half angle of the tapered surface is        in the range 0.025 to 0.075, corresponding to a taper in the        range 5% to 15%.    -   The contact zone is axially located between the threadings and        the free end of the male element.    -   The contact zone is axially located between the threadings and        the free end of the female element.    -   The contact zone is axially spaced from said free end by at        least 3 mm.    -   The cambered surface and the tapered surface are provided on the        element having said free end and on the other element        respectively.    -   The cambered surface extends in the direction of said free end        with a second tapered surface which is tangential to the        cambered surface.    -   The contact zone is axially located between two portions of each        of said threadings.    -   The cambered surface and the tapered surface are formed on the        male and female elements respectively.    -   The male and female elements are free of axial abutment        surfaces.    -   The axial width of the threads of said threadings and/or the        intervals between said threads varies progressively over the        whole of the axial length of said threadings.    -   The axial width of the threads of said threadings and/or the        intervals between said threads varies progressively over the        whole of the axial length of each of said threading portions.    -   Said threadings are tapered.    -   The tapered surfaces having lines joining homologous points on        the different turns as generatrices for the two portions of the        same threading respectively are substantially coincident.    -   The tapered surfaces having lines joining homologous points of        the different turns as generatrices respectively for the two        portions of the same threading are distinct.    -   Said tapered surfaces are radially distant by at least one        thread depth.    -   Said threads have a dovetail profile.    -   The crests and roots of said threads are parallel to the axis of        the threaded connection.    -   The male element is on a great length pipe and its minimum        radial thickness e between the portion of its threading that is        furthest from its free end and said contact zone is at least 60%        of the radial thickness E within the length of the pipe.    -   The connection comprises two contact zones situated respectively        in two of the axial positions as described above.    -   A groove formed at the crest of the male or the female threads        extends along the helical path thereof to allow evacuation of a        lubricant and terminates in an annular discharge space present        between the male and female elements at the end of the threading        or the threading portion concerned, to release the grease        pressure.    -   Said groove has a width of about 0.4 mm.    -   Said groove has a depth of about 0.4 mm.    -   For the male threading and/or the female threading, the loading        flank joins the crest and/or the root of the thread via a        rounded portion the profile of which is substantially formed by        two arcs of circles tangential to each other, the arc adjacent        to the loading flank having a smaller radius of curvature than        the other arc.    -   The radius of the arc adjacent to the loading flank is in the        range 0.1 to 0.2 mm.    -   The radius of said other arc is in the range 0.8 to 1.2 mm.    -   The male and female threadings are non interfering at the thread        roots and crests over all or a portion of the threadings.    -   The male and female threadings are interfering at the thread        roots and crests over all or a portion of threadings.    -   The male and female threadings are interfering at the thread        roots of a first threading and at the thread crests of a second        threading over all or a portion of the threading length whereas        there is a radial clearance between the thread roots of the        second threading and the thread crests of the first threading.    -   Said radial clearance is at least 0.05 mm

The characteristics and advantages of the invention will now bedescribed in more detail in the description below, made with referenceto the accompanying drawings.

FIGS. 1 to 3 are half axial cross sectional views of three threadedtubular connections of the invention intended for oil or gas wells.

FIG. 4 is a partial view on a larger scale of a region of any one of theconnections of FIGS. 1 to 3 close to the free end of the male element.

FIGS. 5 and 6 are partial axial cross sectional views, on a still largerscale, each showing one thread of a connection of the invention.

FIG. 5A shows detail A of FIG. 5 on a larger scale.

FIGS. 7 and 8 show partial axial sectional views each showing a fewturns of the male and female threadings of a connection of the inventionin the made up position for non interfering and interfering threadingsrespectively.

FIG. 9 shows a partial sectional view showing a few turns of the malethreading of a connection of the invention, the axial width of thethreads and that of the intervals between the threads increasing anddecreasing respectively progressively from the free end of the maleelement.

FIG. 10 shows a variation of FIGS. 7 and 8.

The threaded tubular connection shown in FIG. 1 comprises a male tubularelement 1 and a female tubular element 2 each on a great length pipe,not shown in its entirety, and provided with respective taperedthreadings 3, 4 which cooperate together for mutual assembly by makeupof the two elements. The threadings 3, 4 are of a known type with aprogressive variation in the axial thread width and/or the intervalsbetween threads so that a progressive axial interference occurs duringmakeup until a final blocked position.

In accordance with the invention, the fluid seal, both against theinterior of the tubular connection and against exterior media, isensured by two contact zones 5, 6 axially located either side of thethreadings 3, 4 respectively close to the free end 7 of the male elementand the free end 8 of the female element.

The contact zone 5 is shown on a larger scale in FIG. 4. To define saidcontact zone, male element 1 has a cambered surface 11 turned radiallyoutwardly, the diameter of which decreases towards the free end 7. Thesurface 11 has an arc of a circle as a generatrix, with a radius in therange 40 to 80 mm. Facing said cambered surface 11, the female element 2has a tapered surface 12 turned radially towards the interior and with adiameter that decreases in the direction of the free end 7 of the maleelement, i.e. opposite the free end 8 of the female element. The tangentto the vertex half angle of the tapered surface 12 is in the range 0.025to 0.075, i.e. a taper that is in the range 5% to 15%. For illustrativepurposes, the surfaces 11 and 12 are shown in FIG. 4 in their initialgeometric form before makeup but in a relative position corresponding tothe end of makeup of the threaded connection, so that their generatricesintersect one another. Clearly, in reality, progressive deformation ofsaid surfaces occurs during makeup, leading to a seal by radialinterference. The contact zone proper or effective contact zone betweensurfaces 11 and 12 has a certain length and terminates at a point Pwhich is spaced from the free end 7 by a distance d, advantageously atleast 3 mm.

The inventors have discovered that such a contact zone between a taperedsurface and a cambered surface produces a high effective axial contactwidth and a substantially parabolic distribution of contact pressuresalong the effective contact zone, in contrast to contact zones betweentwo tapered surfaces which have two narrow effective contact zones atthe ends of the contact zone.

A contact zone geometry of the invention preserves a good effectivecontact width despite axial positional variations of the assembledelements due to machining tolerances, the effective contact zonepivoting along the cambered section of the cambered surface 11,retaining a parabolic profile for the local contact pressure.

In this regard, it is an advantage that the axial length of the contactsurfaces 11, 12 be greater than the axial positioning variations of theeffective contact zone. Preferably the axial length of the contactsurfaces 11, 12 is greater or equal to 3.5 mm.

This is also the case under service conditions when the stresses towhich the threaded elements of the connection are subjected (inparticular internal or external pressure) induce pivoting of the contactsurfaces 11, 12.

The contact zone geometry of the invention appeared particularlyadvantageous for ensuring the seal when the connection is subjected to ahigh internal pressure after being subjected to a high externalpressure.

Too small a taper (<5%) for the surface 12 induces a risk of galling onmakeup and too high a taper (>15%) necessitates machining tolerancesthat are too narrow.

Too large a radius (>80 mm) for the cambered surface 11 inducesdisadvantages that are identical to those with a taper-to-taper contact.

Too low a radius (<30 mm) for said cambered surface 11 induces aninsufficient contact width.

A distance of at least 3 mm of point P from the free end 7 increases theradial stiffness of the male lip on which the cambered surface 11 isformed and can then increase the contact pressures for a given sectionof material at point P.

The distance d is preferably in the range 4 to 10 mm and in particular,varies with the pipe diameter.

In the example illustrated, the cambered surface 11 of the male elementextends beyond point P and connects tangentially with a tapered surface13 with a vertex half angle of 7° which extends to the free end 7 ofsaid element, which is a flat surface perpendicular to the axis of thethreaded connection. The tapered surface 12 extends beyond point P andis followed by a backoff hollow 15 up to a shoulder 14 of the femaleelement facing end 7 and having a flat annular form perpendicular to theaxis of the threaded connection.

The make up of the elements is not limited by any axial abutmentsurface. In particular surfaces 7 and 14 do not come into abutment anddo not play any role in the cooperation of elements 1 and 2. The backoffhollow between the tapered surface 12 and the shoulder 14 also plays norole in the cooperation of elements 1 and 2.

In contrast, the tapered surface between the cambered surface 11 and end7 can pre-centre the male element as it engages with the female elementprior to makeup without risking damage to the contact surfaces 11 and12.

Further, it can keep a sufficient thickness of material at the end 7 fora given distance between it and the point P with respect to a maleelement wherein the cambered surface 11 would extend to the free end.

At the other end of the cambered surface 11 is an annular groove 17which allows to start the male threading 3.

Preferably, the thickness of the metal on the male element 1 at thebottom of said groove is at least 30% of the thickness of the pipe, toprevent radial deflection towards the axis of said zone.

The contact zone 6 is formed by a cambered surface and a tapered surfacewith the same geometric characteristics as the surfaces 11 and 12 of thezone 5, this time provided on the female element and on the male elementrespectively. The effective contact zone is spaced from the free end 8of the female element by a distance of at least 3 mm. The inventors haveestablished that such a distance can substantially increase the contactpressure in zones 5 and 6. The contact zone 5 provides the fluid-tightseal against the interior of the tubular connection and the contact zone6 provides the fluid-tight seal against external media.

In contrast to threadings 3 and 4 of FIG. 1, which are continuous, eachof the threadings of the tubular connection of FIG. 2 is separated intotwo portions separated from each other in the axial direction, namelyinto a male threading portion 3 a cooperating with a portion of thefemale threading 4 a, and a male threading portion 3 b cooperating witha portion of the female threading 4 b, portions 3 a and 4 a being closerto the free end 8 of the female element and portions 3 b and 4 b beingcloser to the free end 7 of the male element 1. The characteristicpoints of the thread profile, for example the roots of stabbing flanksof the threading portions 3 a and 3 b, are located on substantiallycoincident tapered surfaces and similarly for the threading portions 4 aand 4 b. The term “substantially coincident” means that said taperedsurfaces are separated by a radial distance that does not exceed a fewtenths of millimeters. The progressive variation in the axial width ofthe threads and/or the intervals between the threads occurs here foreach of the threading portions, advantageously over the entire length ofeach thereof.

The seal of the connection of FIG. 2 towards the interior is ensured bya contact zone 5 that is identical to that of FIG. 1. For the sealtowards the exterior, the contact zone 6 of FIG. 1 is replaced by anintermediate contact zone 16 located between the threading portions 3 aand 4 a and the threading portions 3 b and 4 b. The contact zone 16 isdefined by a cambered surface on the male element and a tapered surfaceon the female element with the geometrical characteristics as describedabove for the contact zone 5 in FIG. 1.

For dovetail threads (see below), the minimum radial thickness e of themale element 1 between its threading portion 3 a and the contact zone 16is at least 60% of the radial thickness E in the length of the greatlength pipe 10 of which it forms part. The inventors have establishedthat the geometry of dovetail threads increases the radial stiffness oftheir connection compared with threads that are commonly termed“trapezoidal”, in which the axial width reduces from the thread root tothe crest.

The tubular connection of FIG. 3 differs from that of FIG. 2 by a radialoffset between the threads of the threading portions 3 a and 4 a andthose of the threading portions 3 b and 4 b; the roots and crests of theloading flanks and the stabbing flanks of the threading threads 3 a and4 b are located on tapered surfaces with a larger diameter than those ofthreading portions 3 b and 4 b. Said radial offset is greater than theradial depth of the threads. The fluid-tight seal of said connection isprovided by an interior contact zone 5 similar to the contact zones 5 ofFIGS. 1 and 2 and by an intermediate contact zone 16 similar to that ofFIG. 2.

FIG. 5 is a partial sectional view through an axial plane of a maleelement of a threaded connection 1 of the invention, showing one thread18 of said element. Thread 18 has, in known manner, a dovetail profilewith thread crests and roots that are parallel to the axis of thethreaded connection and thus straight. Further, the loading flank 19 ofthe thread 18 joins the thread crest 20 and the adjacent thread root 21via respective rounded portions the first of which is shown on a largerscale in FIG. 5A. The profile of said rounded portion 22 is composed oftwo arcs of circles 23 and 24, arc 23 being tangential to the flank 19and having a radius R1 in the range 0.1 to 0.2 mm, and arc 24 beingtangential to arc 23 and to the thread crest 20 and having a radius inthe range 0.8 to 1.2 mm. Rounded portion 25 connecting the loading flank19 to the thread root 21 is similar to rounded portion 22, the circulararc with the smaller radius also being adjacent to the flank 19. Theserounded portions reduce the load concentration factor at the base of theloading flanks and thus improve the fatigue behaviour of saidconnection.

FIG. 6 is a view analogous to FIG. 5, showing a groove 28 provided inthe thread crest 20. Said groove extends over the whole of the helicalpath of the male threading to an annular discharge groove 17 (FIGS. 1, 2and 4) at the end of the threading or the threading portion to encourageevacuation of the grease used for lubrication during makeup and as aresult to release the pressure developed by said grease. Groove 28 alsoslightly increases the flexibility of the threads, rendering therelative axial position of the male and female elements less dependenton machining tolerances. In the example shown, groove 28 is connected tothe thread crest via rounded portions. These can be replaced bychamfers.

Rounded portions similar to rounded portions 22 and 25 and/or a groovesimilar to groove 28 can be provided on the female element in additionto or to replace those of the male element. Further, while the roundedportions and the groove are shown separately in FIGS. 5 and 6, they canadvantageously be used together, as shown in FIG. 9. It is also possibleto connect the loading flank of the threads of the male element and/orthe female element to only the thread crest or the root. A furtherpossible variation consists of providing a single contact zone ensuringa seal to both interior and exterior fluids.

The threadings employed in the embodiments can be of any non interferingtype between thread crests and roots, or of the interfering type betweenthread crests and roots.

FIG. 7 shows a male threading 3 and a female threading 4 in the made upposition in the case of non interfering threadings.

The male loading flanks 19 and female loading flanks 30 are in contact,as are the male stabbing flanks 31 and female stabbing flanks 32.

In contrast, there is a clearance between the male thread crest 20 andthe female thread root 33 as well as between the female thread crest 34and the male thread root 21.

Said function is obtained by causing the loading flanks and stabbingflanks to come into contact before any contact between the thread rootsand crests.

It can be seen that by dint of said clearances, a substantial helicalleakage channel 35 exists for fluids, even in the absence of a groove28, the seal being formed by contact surfaces 5, 6, 16.

FIG. 8 shows a male threading 3 and a female threading 4 in the made upposition in the case of interfering threadings; the reference numbersused in FIG. 7 are used to designate similar elements.

The threadings are designed so that the female thread crests come intocontact with the male thread roots and/or the male crests with thefemale thread roots during makeup before contact of the loading flanksand the stabbing flanks.

After said contact between the thread crests and roots, makeup can becontinued until the loading and stabbing flanks come into contact; thethread crests will interfere with the corresponding thread roots.

However, calculations carried out by the inventors show that asufficient seal cannot be guaranteed (gas-tight seal) by threads of thattype of threading because of deformations in the thread faces and theangles between the faces at the end of makeup.

The presence of a groove will also increase the cross section of theleakage channels resulting from said deformations. As was the case withnon interfering threadings, the seal with interfering threadings is madeby the contact surfaces 5, 6, 16.

One advantage of interfering threadings is to use, for a constant pipethickness, higher critical cross sections and as a result, to entrainhigher efficiency of the threaded connection under tension.

FIG. 10 is similar to FIGS. 7 and 8 and again bears the same referencesin the case of interfering threadings at the male thread roots 21 and atthe female thread crests 34, a radial clearance existing between thefemale thread roots 33 and the male thread crests 20. Of course one canprovide for the reverse disposition, i.e. a clearance between the malethread roots 21 and the female thread crests 34 and an interferencebetween the female thread roots 33 and the male thread crests 20.

It is also possible to have 2 or more of the dispositions of FIGS. 7, 8and 10 and of reversed FIG. 10 on the various portions of the threadinglength for example as in the embodiments of FIGS. 2 and 3 where thethreadings are in two portions.

This explains why in FIG. 2 the tapered surfaces of the two threadingportions only need to be substantially coincident, the interferencedifference between the portions inducing a slight radial distancebetween these surfaces.

By way of example, the dispositions of FIGS. 7 and 8 can be producedwith male threads and female threads of a uniform height to 1.16±0.025mm, and the disposition of FIG. 10 by increasing the female threadheight of 1.285±0.025 mm, the male thread height remaining unchanged,which leads to a radial clearance ≧0.075 mm between male crests andfemale roots.

FIG. 9 shows a few turns of the thread 18 of the male threading of aconnection of the invention, separated from each other by a helicalinterval 36. It illustrates the progressive variation, known per se, ofthe axial width of the thread 18 and that of the interval 36,respectively increasing and reducing from the free end of the maleelement, which causes progressive axial interference of the male andfemale threads during makeup.

The embodiments of FIGS. 1 to 3 are relative to threaded assembliesbetween two great length pipes constituted by only one threadedconnection the male and female tubular elements of which are located atthe end of the great length pipes.

Such threaded assemblies can be of the “flush” type (the externaldiameter of both elements of the threaded connection is that of thepipe) or of the “semi-flush” type also known as “slim-line” (theexternal diameter of the female element is greater by a few percent thanthe diameter of the male element).

The invention can also apply to threaded and coupled assemblies betweentwo great length pipes, those coupled assemblies being constituted bytwo tubular threaded connections, the female elements being positionedopposite on a coupling whereas the male elements are produced on greatlength pipes.

1-31. (canceled)
 32. A threaded tubular connection comprising: a maletubular element comprising a male threading and a female tubular elementcomprising a female threading that cooperates by makeup with the malethreading, axial width of the threads of the threadings and/or intervalsbetween the threads varying progressively along an axis of connectionover at least a portion of an axial length of the threadings, such thatthe threads of each threading are housed with an axial clearance in theintervals of the other threading at a start of makeup, the clearanceprogressively decreasing until it becomes zero at the end of makeup; andat least one contact zone axially separated from the threadings in whichthe male and female elements are in sealed contact by bearing surfacesrespectively constituted by a cambered surface and by a tapered surface.33. A threaded connection according to claim 32, in which the camberedsurface has a generatrix with a radius of curvature in the range 30 to80 mm.
 34. A threaded connection according to claim 32, in which thetangent to the vertex half angle of the tapered surface is in the range0.025 to 0.075.
 35. A threaded connection according to claim 32, inwhich the contact zone is axially located between the threadings and afree end of the male element.
 36. A threaded connection according toclaim 32, in which the contact zone is axially located between thethreadings and a free end of the female element.
 37. A threadedconnection according to claim 35, in which the contact zone is axiallyspaced from the free end by at least 3 mm.
 38. A threaded connectionaccording to claim 35, in which a cambered surface and a tapered surfaceare provided on the element having the free end and on the other elementrespectively.
 39. A threaded connection according to claim 38, in whichthe cambered surface extends in the direction of the free end with asecond tapered surface that is tangential to the cambered surface.
 40. Athreaded connection according to claim 32, in which the contact zone isaxially located between two portions of each of the threadings.
 41. Athreaded connection according to claim 40, in which a cambered surfaceand a tapered surface belong to the male and female elementsrespectively.
 42. A threaded connection according to claim 32, in whichthe male and female elements are free of axial abutment surfaces.
 43. Athreaded connection according to claim 32, in which the axial width ofthe threads of the threadings and/or the intervals between the threadsvaries progressively over the whole of the axial length of thethreadings.
 44. A threaded connection according to claim 40, in whichthe axial width of the threads of the threadings and/or the intervalsbetween the threads varies progressively over the whole of the axiallength of each of the threading portions.
 45. A threaded connectionaccording to claim 40, in which the threadings are tapered.
 46. Athreaded connection according to claim 45, in which the tapered surfaceshaving lines joining homologous points on different turns asgeneratrices for two portions respectively of the same threading aresubstantially coincident.
 47. A threaded connection according to claim45, in which the tapered surfaces having lines joining homologous pointson different turns as generatrices for two portions of the samethreading respectively are distinct.
 48. A threaded connection accordingto claim 47, in which the tapered surfaces are radially distant by atleast one thread depth.
 49. A threaded connection according to claim 32,in which the threads have a dove-tail profile.
 50. A threaded connectionaccording to claim 49, in which crests and roots of the threads areparallel to the axis of the threaded connection.
 51. A threadedconnection according to claim 50, in which the male element is on alength pipe and its minimum radial thickness between a portion of itsthreading furthest from its free end and the contact zone is at least60% of a radial thickness within the length of the pipe.
 52. A threadedconnection according to claim 32, in which the connection comprises twocontact zones.
 53. A threaded connection according to claim 32, in whicha groove formed at the crest of the male threads or the female threadsextends along a helical path thereof to allow evacuation of a lubricantand terminates in an annular discharge space present between the maleand female elements at the end of the threading or the threading portionconcerned.
 54. A threaded connection according to claim 53, in which thegroove has a width of about 0.4 mm.
 55. A threaded connection accordingto claim 54, in which the groove has a depth of about 0.4 mm.
 56. Athreaded connection according to claim 50, in which, for the malethreading and/or the female threading, a loading flank joins the crestand/or the root of the thread via a rounded portion having a profilethat is substantially formed by two arcs of circles tangential to eachother, the arc adjacent to the loading flank having a smaller radius ofcurvature than the other arc.
 57. A threaded connection according toclaim 56, in which the radius of the arc adjacent to the loading flankis in the range 0.1 to 0.2 mm.
 58. A threaded connection according toclaim 57, in which the radius of the other arc is in the range 0.8 to1.2 mm.
 59. A threaded connection according to claim 50, in which themale and female threadings are non interfering at the thread roots andcrests over all or a portion of the threadings.
 60. A threadedconnection according to claim 50, in which the male and femalethreadings interfere at the thread roots and crests over all or aportion of the threadings.
 61. A threaded connection according to claim50, in which the male and female threadings interfere at the threadroots of a first threading and at the thread crests of a secondthreading over all or a portion of the threading length, whereas thereis a radial clearance between the thread roots of the second threadingand the thread crests of the first threading.
 62. A threaded connectionaccording to claim 61, in which said radial clearance is at least 0.05mm.